Variable power optical system and image-recording device

ABSTRACT

A variable power optical system composed of a first optical part, a second optical part, and a third optical part, with the first optical part being movable with respect to the second and third optical parts to change the focal length of the entire system. The first optical part is movably held between the second optical part and the third optical part. The first optical part moves in the direction perpendicular to the optical axis over a distance between the position on the optical system of the entire system and the position of retraction from the optical axis of the entire system.

CROSS REFERENCES TO RELATED APPLICATIONS

This present application is a Continuation Application of the patentapplication Ser. No. 10/579,210, filed Feb. 1, 2007, now U.S. Pat. No.7,554,749, which is a National Phase of International Application No.:PCT/JP05/016725, filed Sep. 12, 2005, which claims priority fromJapanese Patent Applications JP 2004-305437 filed in the Japanese PatentOffice on Oct. 20, 2004, the entire contents of which being incorporatedherein by reference.

TECHNICAL FIELD

The present invention relates to a variable power optical system and animage-recording device with the variable power optical system. Thevariable power optical system changes in focal length as its movableoptical parts move from one position to another, and the image-recordingdevice has a simplified and miniaturized mechanism.

BACKGROUND ART

There is a recent trend for mobile equipment to be equipped with a smallcamera module. Attempts are being made to develop a further miniaturizedcamera module having improved and diversified capabilities.

Such capabilities include a mechanism that changes the focal length asan afocal lens (with an angular magnification smaller than 1) isattached to or detached from the subject side of the image-forming lens.This mechanism is applicable to the built-in camera in the portabletelephone or computer or the monitoring camera. An example of thevariable power optical system is disclosed in Japanese Patent Laid-openNo. Hei-7-20367. It has an afocal system consisting of a negative lensgroup and a positive lens group that are placed a certain distanceapart. The afocal system is held in a lens barrel which has an lateralopening. The afocal system (which is placed in front of theimage-forming lens) is moved out of the optical axis as it is turnedthrough 90°. In this state, the lateral opening in the lens barrelfunctions as a window that permits the image-forming lens to take aphotograph by itself.

The camera module to be built into the portable equipment needsimprovement in its performance without its mechanism getting complex andlarge and its power consumption increasing. In other words, the lenssystem of the camera in the portable telephone or notebook personalcomputer is restricted in its depth, because the camera has to fit intothe thickness of the portable telephone or the thickness of the cover ofthe personal computer. In addition, the camera that relies on a powersupply from the battery needs a means to save power consumption.

DISCLOSURE OF THE INVENTION

Unfortunately, the conventional system presents difficulties inminiaturization and cost reduction because of its lens driving mechanismand lens barrel structure that cannot be simplified.

Any conventional camera module, for example, needs a complex drivingmechanism or actuator to switch between the wide-angle lens and thetelephotographic lens. However, such a mechanism or actuator is toolarge to permit the camera module to be built into the recent smallmobile equipment. Moreover, the camera module with a complex mechanismis vulnerable to drop impact and hence is unsuitable to the small mobileequipment that needs strength for carrying. Also, the complex mechanismtakes a long time for assembling (which increases the production cost)and needs troublesome maintenance and quality assurance.

It is an object of the present invention to provide a new optical systemwhich is capable of changing (or switching) its focal length without anycomplex mechanism and which is small in size and low in production cost.

The present invention, which was completed to address theabove-mentioned problems, is directed to a variable power optical systemcomposed of a first optical part for refraction, a second optical partfor reflection or transmission, and a third optical part for refraction,with the first optical part being movable with respect to the second andthird optical parts to change the focal length of the entire system,wherein the second optical part or the third optical part has a guidewhich is in contact partly with the first optical part in such a way asto restrict its moving direction and the first optical part is movablyheld between the second optical part and the third optical part.

The present invention is directed also to a variable power opticalsystem composed of a movable optical part for refraction and a plasticsstationary optical part which functions as a base to support the movableoptical part and has a lens formed integrally therewith, with themovable optical part being movable with respect to the stationaryoptical part to change the focal length of the entire system, whereinthe stationary optical part has a guide formed integrally therewithwhich is in contact partly with the movable optical part in such a wayas to restrict its moving direction.

The above-mentioned optical system according to the present inventionoffers the advantage of eliminating the necessity of separately adding aguide to move the first optical part or the movable optical part. Inother words, it is possible to support the first optical part or themovable optical part by utilizing the existing optical part (which isoptically essential) if the second or third optical part is providedwith the guide for the first optical part or the stationary optical partis formed integrally with the guide for the movable optical part.

The present invention makes it possible to realize the function ofcontrolling and switching the focal length without requiring any complexmechanism to move the first optical part or the movable optical part.This is desirable for miniaturization and cost reduction.

According to a preferred embodiment of the variable power optical systemmentioned above, the first optical part has a first lens and a secondlens and constitutes, in combination with the second optical part, anafocal system such that the first optical part moves in the directionperpendicular to the optical axis of the first and second lenses over adistance between the position on the optical system of the entire systemand the position of retraction from the optical axis of the entiresystem. This structure saves the space (including the gap between theoptical parts) necessary for the first optical part to move, which isdesirable for miniaturization. In addition, the variable power opticalsystem mentioned above may be modified such that the light that haspassed through the first lens is reflected by the second optical part,with its optical path diverted at right angles, and then passes throughthe second lens. This structure reduces the depth and makes the opticalsystem adaptable to any equipment with a limited thickness.

To save cost and reduce the number of parts, it is desirable to make thefirst optical part in one step by integral molding from plastics.

The plastics stationary optical part mentioned above should preferablybe formed integrally with the guide for the movable optical part. Thiseffectively simplifies the structure. In addition, preferably, thestationary optical part should preferably have a recess to receive thelens at the opposite side of the guide. The stationary optical part withsuch a recess functions as a lens holding member. (This eliminates thenecessity for providing the lens holding member.)

The variable power optical system according to the present invention mayhave a movable lens for the light which has passed through the movableoptical part and the stationary optical part so that the movable lenstogether with the lens of the stationary optical part constitute theimage-forming optical system and the stationary optical part is providedwith a mechanism to drive the movable lens. This structure determinesthe optical position of the movable optical part and the movable lens inconformity with the stationary optical part, thereby effectivelyassuring accuracy.

The variable power optical system according to the present invention maybe applied to an image-recording device. In this case it contributes tosize reduction despite its additional functions, such as the ability tochange the focal length. In addition, it simplifies the mechanism andhelps reduce the number of parts and assembling steps, which effectivelycontributes to quality assurance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing the basic structure of thevariable power optical system according to the present invention.

FIG. 2 is a front view of the variable power optical system according tothe present invention.

FIG. 3 is a sectional view of the variable power optical systemaccording to the present invention.

FIG. 4 is a sectional view of the optical part G1.

FIG. 5 is an exploded perspective view, with constituent parts partiallycut away.

FIG. 6A is a diagram showing the arrangement of lenses for wide-anglephotography and telephotography.

FIG. 6B is a diagram showing the arrangement of lenses for wide-anglephotography and telephotography.

FIG. 7 is an external view showing one example of the present invention.

FIG. 8 is a perspective view showing important parts of one example ofthe present invention.

FIG. 9 is a diagram illustrating the movable lens L3 and its guidemechanism.

FIG. 10 is a perspective view showing important parts of the opticalsystem arranged for wide-angle photography.

FIG. 11 is a perspective view showing important parts of the opticalsystem arranged for telephotography.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention may be suitably applied to any equipment which islimited in space inside the enclosure (or which is limited inthickness).

The camera module is becoming larger and larger in size for improvedperformance and diversified functions, whereas the portable equipment tocarry it needs miniaturization. The present invention is designed for aminiaturized, variable power optical system suitable for the cameramodule with two focal lengths for wide-angle photography andtelephotography which is to be mounted on a mobile communicationsterminal (such as portable telephone) or a mobile information processingterminal (such as portable computer and PDA).

FIG. 1 is a schematic diagram showing the basic structure of thevariable power optical system according to the present invention.

The variable power optical system 1 has the first optical part “G1” forrefraction, the second optical part “G2” for reflection or transmission,and the third optical part “G3” for refraction. It permits G1 to movewith respect to G2 and G3, thereby changing the focal length of theentire system continuously or stepwise. Incidentally, an actuator or amanual sliding mechanism may be used to move G1.

In the case where G2 and G3 are stationary optical parts, a conceivablemechanism to move G1 in the direction perpendicular to the optical axisx is a guide which is composed of rods or shafts fixed to the lensbarrel (not shown) and extending parallel to each other. The guidemembers are passed through holes formed in G1, so that they slidablyhold G1. This mechanism, however, needs a complex structure as well as alarge space, and hence it hinders miniaturization.

In the present invention, this problem is tackled by providing G2 or G3with a guide which restricts the direction of movement of G1 whileremaining in contact with G1 b (which is a constituent member of G1).This structure saves the number of parts of the guide and movablysupports G1 between G2 and G3. (A detailed description follows.)

It is possible to simplify the structure if G1 is constructed of G1 aand G1 b and G1 b is slidably held between G2 and G3. Incidentally, G1 bmay be a lens or a transmitting optical part.

The optical system according to the present invention does not need eachlens to have a guide for movement of G1. Instead, G1 can be supported bymeans of the existing optical part.

The following constructions are given for G1.

Incidentally, G1 may be constructed by combining G1 a and G1 b, whichhave been formed previously and separately, or by integrally forming G1a and G1 b from plastics.

FIGS. 2 and 3 are diagrams showing the structure of a video cameramodule provided with the variable power optical system according to thepresent invention. This camera module has two switchable focal lengthsfor wide-angle photography and telephotography.

Both FIG. 2 and FIG. 3 show the structure of the lens for wide-anglephotography. FIG. 2 is a front view, and FIG. 3 is a sectional view.

The first optical part G1 has a first lens W1 (with negative refractingpower) and a second lend W2 (with positive refracting power), both ofwhich are single lenses in this example. (Single lenses are preferablefor simple structure with a minimum number of parts, although compoundlenses are also acceptable.) Preferably, W1 should be a concave meniscuslens, with its strong concave surface facing the subject, and W2 shouldbe a convex lens. (The combination of W1 and W2 mentioned above issuitable for a simple, small afocal system. At least one surface ofthese lenses preferably should be aspherical for aberration correctionin the afocal system.)

Preferably, G1 should be a single part molded from transparent plasticsfor cost saving and parts reduction, so that it can be molded in onestep. G1 in this example has an L-shaped cross section, so that W1 andW2 have optical axes crossing each other at right angles.

FIG. 4 is a sectional view of the optical part G1 consisting of W1 andW2 which are integrally molded from plastics.

The molding of plastic lenses usually employs a mold which opens in thedirection of the optical axis at the time of demolding. However, themolding of the complex lens shown in FIG. 4 employs a mold which opensin the directions indicated by arrows A and B (at an angle of about 45°with respect to the optical axes of W1 and W2) at the time of demolding.

In FIG. 4, rW1 a and rW1 b denote respectively the incident surface andthe emergent surface of the first lens W1. Also, in FIG. 4, rW2 a andrW2 b denote respectively the emergent surface and the incident surfaceof the second lens W2.

The surfaces rW1 a and rW2 a are formed by a mold which opens in thedirection of arrow A. The surfaces rW1 b and rW2 b are formed by a moldwhich opens in the direction of arrow B. To ensure good demolding, theperiphery of the lens should be free of undercuts which prevent the moldfrom opening smoothly in the directions of arrows A and B.

FIG. 5 shows the shapes of G1, G2, and G3 in perspective.

The second optical part G2 is a stationary mirror or prism to bend theoptical path by reflection. G2 in combination with G1 constitutes anafocal system. G2 may be a right-angle prism of glass having a highrefractive index. This helps miniaturize the afocal system because theprincipal ray inclines less toward the optical axis in the prism.

The third optical part G3 functions as a base to support G1. It is astationary plastics optical part in which the lens L1 is integrallyformed.

The part 2 of G1, in which W2 (corresponding to G1 b mentioned above) isformed, is held between G2 and G3. G1 is held by G3 such that it movesin the direction of arrow M in FIG. 2. In other words, the part 3(facing G3) of the part 2 is in contact with the rail-like guide 4formed on G3, and the part 3 is in contact with G2. Incidentally, theguide 4 is formed on G3 for easy fabrication in this example; however,it also is possible to form the guide on G2.

The direction of movement of G1 (as a movable optical part) isrestricted by the guide 4 of G3, so that G1 is made to move in thedirection perpendicular to the optical axis of W1 and W2. To be moreprecise, G1 moves between one position (indicated by a solid line inFIG. 2) and the other position (indicated by a chain line in FIG. 2).The first position (for wide-angle photography) coincides with theoptical axis of the entire system) and the second position (fortelephotography) is away from the optical axis of the entire system.This structure saves space for the movement of G1 and hence is desirablefor miniaturization.

Preferably, G3 should be made of clear synthetic resin, so that theguide 4 is integrally formed. G3 has a recess 5 (to receive the lens L2)in the opposite side of the guide 4, so that L2 is fitted into and fixedto the recess. Thus, G3 functions not only as a base for G1 but also asa lens holding member.

The light which has passed through W1 is reflected by the oblique planeof G2 and diverted at right angles, so that it passes through W2, L1,and L2.

The light which has passed through G1, G2, and G3 passes through themovable lens L3 for autofocusing (AF). (Incidentally, G3 has a mechanismto guide and drive L3 as mentioned later.) L3 together with L1 and L2constitute the image-forming optical system L.

The image-forming optical system L is not specifically restricted aslong as it has an angle of view slightly smaller than the standard lensand is comprised of lenses that permit easy aberration correction forthe diaphragm placed in front of them. For example, it may be comprisedof tree lenses constituting three lens groups as shown in FIG. 3. Thefirst lens is a convex lens L1 (having an aspherical surface), with itsconvex surface facing the subject. The second lens is a concave meniscuslens L2, with its concave surface facing the image. The third lens is aconvex lens L3. This optical system is simple in structure and yet isminiaturized to such an extent that the overall length from the sidefacing the subject to the image is approximately equal to the focallength. In addition, with W1 and W2 (as the wide conversion lens)attached for wide-angle photography, it has a negative Petzval sum, butwithout W1 and W2, it has an adequate positive Petzval sum. Thiseffectively prevents the curvature of field from fluctuating as thefocal length is switched.

The light which has passed through the image-forming system L thenpasses through the filter F and reaches the image forming plane IMG,where there is arranged a solid imaging device, such as a CCD (ChargeCoupled Device) and a CMOS (Complementary Metal Oxide Semiconductor).

The above-mentioned G1, G3, and L3 may be made of clear plastics such asacrylic resin, polycarbonate, and polyolefin, which cost less and permiteasy design. Of these plastics, cyclo-olefin polymer (“ZEONEX” from ZeonCorporation) is desirable because of its good optical properties andmachinability. It permits an aspherical surface for aberrationcorrection to be formed thereon easily. The prism G2 is made of glass,and the lens L2 (which is held in the recess 5 of G3) also is made ofglass.

FIG. 6( a) shows the lens arrangement for wide-angle photography.

The lenses and prism are arranged in the order of W1, G2, W2, and L(starting from the object side). The first three members constitute theafocal system producing an angle magnification smaller than 1. The lightwhich has passed through W1 is reflected by the reflecting surface ofthe prism for a 90° diversion. Then it passes through W2, L(image-forming optical system), and F (filter) to reach the receivingsurface of the imaging device.

FIG. 6( b) shows the lens arrangement for telephotography.

This lens arrangement results after W1 and W2 have moved in thedirection perpendicular to the optical axis of the entire system (or inthe direction perpendicular to the paper) and retreated to the positionaway from the light path of the image-forming optical system L. Thelight incident on G2 is deflected through 90°, and the deflected lightreaches the receiving surface of the imaging device through theimage-forming optical system L and filter F.

Thus, the variable power optical system according to the presentinvention is constructed such that the focal length of the entire systemvaries, with the angle magnification remaining smaller than 1, as G1moves between two positions, one where W1 and W2 are on the optical axisof the entire system and the other where W1 and W2 are away from theoptical axis of the entire system.

Moreover, the variable power optical system according to the presentinvention has a reduced depth (in the direction of the optical axis ofW1) owing to the stationary optical part (G2) which deflects the opticalpath between W1 and W2. (The depth is indicated by “d” in FIG. 3.) Thereduced depth permits the optical system to be adapted to a mobile phonewith limited dimensions.

The variable power optical system according to the present invention isconstructed such that W1 and W2 move in the direction approximatelyperpendicular to their optical axis. This structure saves the space formovement of W1 and W2 more than the structure which is designed to turnthe lens barrel, and hence it is small in size and readily adaptable toa mobile phone with limited dimensions.

Modes of the moving means of G1 include the following.

A mode in which a manual mechanism is used; and

A mode in which an actuator is used.

The manual mechanism may be comprised of an energizing means (such aselastic body and magnet) that keeps G1 at the position for wide-anglephotography and a locking means that keeps G1 at the position fortelephotography when a knob or lever attached to G1 is operated toretreat G1. When the lock is released, G1 returns to the position forwide-angle photography. The manual mechanism needs no electric power andhence is suitable for any equipment that requires an energy savings andalso is suitable for the simple and miniaturized mechanism.

The actuator may employ an elastic member 6 of a shape-memory alloy(which is schematically represented by a spring in FIG. 2), so that theelastic member extends or contracts as it is electrically energized,thereby moving G1. The elastic member 6 has its one end attached to G1and the other end fixed. It keeps G1 at the position for wide-anglephotography and moves (retreats) to the position for telephotography asit contracts upon electrification. The actuator also may employ anelectromagnetic mechanism for attraction and repulsion or a gearmechanism driven by a power unit. Any complex mechanism should beavoided.

In the case where G2 is a prism or mirror, G1 can be supported by meansof an optically necessary part. However, the present invention may beapplied to any system which does not use a prism or mirror. For example,G1 may be comprised of W1 and W2 that are placed a certain distanceapart and hence assume a U-shaped cross section. In this case, G1 ispartly held between a transparent member (corresponding to G2) and G3 sothat it is movable. (The transparent member may be integrally formedwith G3, so that G1 can be supported by a single part.)

The above-mentioned mechanism may be modified such that G1 itself isreplaced by any one of interchangeable parts according to need insteadof providing the means to move G1. In this case, G1 is partly heldbetween G2 and G3 so that it functions as an interchangeable lens.

EXAMPLES

FIGS. 7 to 11 show an example of the portable equipment (such as mobilephone) to which the present invention is applied.

FIG. 7 shows the external appearance of the image-recording device 7,which is comprised of the main body 8 and the camera module 9 mountedthereon.

The main body 8 has a slot 10 formed in its side wall. Projectingthrough the slot 10 is a slidable knob 11 to move the movable opticalpart corresponding to G1 mentioned above manually. The camera module 9has the same optical constitution as mentioned above. That is, it iscomprised of the first lens W1, the optical part G2 to divert theoptical path, the second lens W2, and the image-forming optical system L(having a field angle of about 32°), with the first three componentsconstituting an afocal system having an angle magnification of 0.5.

FIG. 8 is a perspective view showing the important parts of theimage-recording device 7 arranged for wide-angle photography.

The optical part G1 has a projection 12, to which a knob 11 is fixed.The knob 11 projects from the casing 13 of the main body 8, with itspart passing through the slot 10.

The optical part G2 is a triangular prism. Between the prism and G3,part of G1 is slidably held. In other words, G3 has the guide 4 (guiderail), and the part 2 of G1 comes into contact with the guide 4. As theknob 11 is slid along the slot 10, G1 is moved in the prescribeddirection, for example, it is moved from the position for wide-anglephotography (as shown) to the position for telephotography.

The ends of G2 (prism) and G3 are fixed to the side plates 14 and 14,which are fixed to the casing 13.

The movable lens L3, as a constituent of the image-forming opticalsystem L, is comprised of the lens 15 and the frame 16, which are moldedintegrally (to save the number of parts and assembling steps). The frame16 is movably supported by the shafts 17 and 18 so that it moves alongthe optical axis.

The guiding shafts 17 and 18, which extend along the optical axis fromthe optical part G3, are connected to the imaging device 22 (mentionedlater). FIG. 9 is a schematic sectional view showing the frame 16 andthe shafts 17 and 18. The frame 16 for the movable lens L3 has a hole 19and a notch 20, which are symmetrically arranged with respect to thelens center. The shaft 17 passes through the hole 19, and the shaft 18fits into the notch 20. The frame 16 also has a projection 16 a, whichis driven by an actuator 21 so that the movable lens L3 moves along theshafts 17 and 18.

The above-mentioned structure permits G3 (as the stationary opticalpart) to be provided with a mechanism (and guide) to drive the movablelens L3. This mechanism determines the accuracy of the lens system(including L3, L2, and L1) and hence contributes to the accuracy ofassembling. It follows, therefore, that the optical positions of W2, L1,L2, and L3 are determined by a single stationary optical part, and thisis desirable for the assurance of accuracy.

The imaging device 22 is placed at the image-forming plane of theimage-forming optical system L. It transmits its output signals to thecamera signal processing unit (not shown).

FIGS. 10 and 11 are perspective views showing the important parts of G1,G2, G3, L3 and the imaging device 22. In FIG. 10, G1 is positioned forwide-angle photography (with a focal length of 35 mm, for example), andin FIG. 11, G1 is positioned for telephotography (with a focal length of70 mm, for example).

In the case shown in FIG. 10, G1 is moved to one end (right side) of thespace between G2 and G3, so that the entire system is comprised of W1,G2, W3, and L, the former three constituting the afocal system and thelast one constituting the image-forming optical system.

In the case shown in FIG. 11, G1 is moved to the other end (left side)of the space between G2 and G3, so that the entire system is comprisedof G2 and L.

The above-mentioned structure may be applied to a mobile phone with abuilt-in camera, which is comprised of the following components.

-   -   CPU (Central Processing Unit) and system controller.    -   ROM (Read Only Memory), RAM (Random Access Memory), and        auxiliary memory.    -   Liquid crystal display and its controller.    -   Cameral module and its controller.    -   Voice signal processing unit.    -   Communications processing unit.

The above-mentioned constituents are connected to one another throughbuses. For example, the control unit of the camera module sends controlsignals to the actuator 21 to drive the movable lens L3. The cameramodule may be equipped with a sensor to detect the position of theoptical part G1 or the knob 11, so that the control unit of the cameramodule knows whether G1 is positioned for wide-angle photography ortelephotography.

The control unit of the camera module performs image data compression onthe static images and dynamic images obtained by the variable poweroptical system and imaging device, thereby converting them into data inthe format of JPEG (Joint Photographic coding Experts Group) or MPEG(Moving Picture Experts Group). The compressed image data is storedtemporarily in RAM and then transferred to a recording medium (such asmemory card) for image data storage or displayed on the monitor on themain body.

The camera may also record voice data through the microphone insynchronism with photographing, and the recorded voice data is sent tothe data recording unit or speaker through the voice processing unit(audio codec).

The image and voice data may be transmitted, according to need, to theexternal information equipment by infrared rays or through wirelesscommunications interface. The communications control unit transmits andreceives radio waves to and from the radio station through the antenna.

Owing to its reduced depth, the camera module with the variable poweroptical system according to the present invention can be mounted easilyon any equipment, such as a mobile phone, which is limited in size.

The above-mentioned structure offers the following advantages.

-   -   It can be applied to an optical system which needs the switching        of focal length for wide-angle photography, telephotography, or        close-up photography without requiring any complex mechanism,        with the optical system remaining small in size.

It permits the optical part (which is essential in the optical system)to function as a support for the lens and the lens moving mechanism,thereby eliminating the necessity of adding a guide or the like. Thiseffectively simplifies the mechanisms and reduces the number of parts.

Needing no actuator or power source to change the focal length, it issimple in structure and suitable for small mobile equipment with lesspower consumption.

1. A variable power optical system comprising: a first optical part, asecond optical part, and a third optical part, with the first opticalpart being movable with respect to the second and third optical parts tochange the focal length of the variable power optical system, whereinthe second and the third optical parts are fixed in a stationary staterelative to each other and relative to the first optical part, whereinthe first optical part is movably held between the second optical partand the third optical part, and wherein the first optical part moves inthe direction perpendicular to an optical axis of the variable poweroptical system over a distance between an initial position on thevariable power optical system and a second position of retraction fromthe optical axis.
 2. The variable power optical system according toclaim 1, wherein the second optical part or the third optical part has aguide which is in contact partly with the first optical part in such away as to restrict its moving direction.
 3. The variable power opticalsystem according to claim 1, wherein the first optical part has a firstlens and a second lens and constitutes, in combination with the secondoptical part, an afocal system.
 4. The variable power optical systemaccording to claim 3, wherein a light that has passed through the firstlens is reflected by the second optical part, with its optical pathdiverted at right angles, and then passes through the second lens. 5.The variable power optical system according to claim 1, wherein thefirst optical part is a molded product formed from a plastics material.6. An image-recording device comprising: an image-forming optical systemand an imaging device placed at a focal plane with the image-formingoptical system being constructed such that one optical part is moved tochange a focal length of the image-forming optical system, wherein theimage-forming optical system is composed of a first optical part, asecond optical part, and a third optical part, with the first opticalpart being movable with respect to the second and third optical parts tochange the focal length of the image-forming optical system, wherein thesecond and the third optical parts are fixed in a stationary staterelative to each other and relative to the first optical part, whereinthe first optical part is movably held between the second optical partand the third optical part, and wherein the first optical part moves inthe direction perpendicular to an optical axis of the image-formingoptical system over a distance between an initial position on thevariable power optical system and a second position of retraction fromthe optical axis.
 7. The image-recording device according to claim 6,wherein the second optical part or the third optical part has a guidewhich is in contact partly with the first optical part in such a way asto restrict its moving direction.
 8. The image-recording deviceaccording to claim 6, wherein the first optical part has a first lensand a second lens and constitutes, in combination with the secondoptical part, an afocal system.
 9. The image-recording device accordingto claim 8, wherein a light that has passed through the first lens isreflected by the second optical part, with its optical path diverted atright angles, and then passes through the second lens.
 10. Theimage-recording device according to claim 6, wherein the first opticalpart is a molded product formed from a plastics material.